With the use of ceramic antenna systems, so-called ringing in the near zone of the antenna system occurs in the C-band (6.3 GHz). This ringing is due to slowly decaying ripples after antenna coupling in the direction of the time axis or distance axis. In the C-band this ringing is relatively pronounced. However, such ringing is also experienced in the so-called K-band (26 GHz) or at higher or lower frequencies.
The increased ringing is system-related and is primarily caused by the transition of air to ceramic material. At these transition points (ceramic material-air or air-ceramic material) a part of the electromagnetic waves is reflected as a result of the large discontinuity in the dielectric constant (dielectric permittivity). From the part that enters the ceramic material, a part is again reflected at the next transition etc. Since the ceramic material provides only little attenuation, it takes a relatively long time until the waves in the system have “fizzled out”. This effect manifests itself in the so-called antenna ringing.
In applications at temperatures exceeding 200° C., or in applications involving high pressure, it may not be possible to use an antenna system comprising a process separation device made of polytetrafluoroethylene (PTFE) as is otherwise common, because said process separation device made of PTFE would be destroyed by the high temperature or the high pressure. In such applications, according to the present state of the art, process separation is implemented on a ceramic basis (e.g. aluminium oxide (Al2O3) with a dielectric permittivity value of approx. 9.9), which may result in significantly more pronounced ringing in the near zone. In this case the term “near zone” refers to a distance of up to 10 m, depending on the antenna system and the frequency used.
As a result of the strong ringing, in many applications near-zone measuring is either not possible or insufficiently accurate. In the case of media involving low dielectric permittivity a measurement is often not possible.
Since this increased antenna ringing is to a large extent construction-related and may thus not be avoidable, it has to be “attenuated” by corresponding measures.